The present invention relates to printed circuit boards and, more specifically, to programmable printed circuit boards which are encoded by selectively burning out circuit runs.
With increasing automation in the field of analytical chemistry, it becomes more important for instrumentation used in such applications to be able to sense not only the characteristics of the sample under examination but also its own operating status, condition and configuration.
The present invention, as described herein, has application where it is desired that an instrument, such as a spectrophotometer, operate with a plurality of lamps; further, that such lamps can be brought into the use position automatically and have the apparatus recognize the type of lamp in the use position. In this way the apparatus can effect automatic internal adjustments, such as grating position and lamp power level, in accordance with the lamp being used. It is a further requirement that such a lamp recognition device be reliable and inexpensive to fabricate.
Prior art devices provide for automatic recognition of a lamp by optically, magnetically or mechanically encoding the lamp with its atomic element and operating current. Such encoding schemes are expensive to assemble to the lamp and have the further drawback of requiring expensive and complex apparati to read the information contained in their respective media.
Prior art devices also have provided lamps wherein an electrical network, integral to the lamp, is read by the spectrophotometer to provide information as to the atomic element of the lamp and its operating current. The electrical circuit is, preferentially, resistive, is unique to each lamp and must be individually fabricated as an integral part of each lamp. Such an approach is inherently inflexible and costly to produce.
It was considered that a small printed circuit (pc) board could be integrated into the lamp plug, such pc board being pre-encoded, prior to assembly, with a code indicative of the lamp to which the plug is attached. By pre-encoding the pc board, the assembly costs are great, since a supply of pc boards for each lamp type has to be stocked, then matched with the proper lamp during assembly.
Alternatively, the plug could be hard-wired with the appropriate code. While this would eliminate the problem of having to stock a large quantity of pc boards, it would result in high assembly costs.
Another possible solution is to provide a pc board wherein certain of the circuit runs are cut during assembly so as to encode the lamp type to provide instrument recognition of its element. Such an approach also leads to high assembly costs.
The present invention overcomes the disadvantages of the foregoing approaches by providing a printed circuit board which is integral with the lamp plug and is quickly, accurately and simply encoded following its assembly with the lamp.